1. Field of the Invention
The present invention generally relates to an image defect correcting circuit for a solid state imager which corrects image defect involved in an output image of a solid state image pickup element. More particularly, this invention relates to an image defect correcting circuit for a solid state imager in which an image defect involved in an output image of a solid state image pickup element is corrected in accordance with an image defect position information generated on the basis of an output of the solid state image pickup element.
2. Description of the Prior Art
Of pixels (picture elements) of a solid state image pickup element, a pixel, which is not operated normally due to lattice defect or the like, is what might be called a blemish. Of the blemishes, a blemish produced by a pixel which generates a large voltage as compared with other normal pixels, is called a white blemish, while a blemish produced by a pixel which generates a small voltage or which produces substantially no voltage as compared with other normal pixels, is called a black blemish.
FIGS. 1A to 1F show, when an iris of a so-called three CCD (charge coupled device) type television camera is closed, respectively, its solid state image pickup elements r, g and b and red, green and blue video signals Vr, Vg and Vb output from these solid state image pickup elements r, g and b.
As is clear from FIGS. 1A to 1F, since the solid state image pickup elements g and b shown in FIGS. 1C and 1E have no blemish, the video signals Vg and Vb from these solid state image pickup elements g and b have level corresponding to the level under the condition such that no light is incident thereon as shown in FIGS. 1D and 1F. On the other hand, the solid state image pickup element r shown in FIG. 1A has a white blemish at a position shown by a solid arrow in FIG. 1A. Accordingly, as shown in FIG. 1B, in the video signal Vr from this solid state image pickup element r, the level thereof becomes high at the position of the video signal Vr corresponding to the pixel shown by the solid arrow in FIG. 1A.
FIGS. 2A to 2F show, respectively, solid state image pickup elements r, g and b and red, green and blue video signals Vr, Vg and Vb output from these solid state image pickup elements r, g and b when the three CCD television camera similarly to FIG. 1 is used and a white diffusion plate (illuminated in the direction opposite to the camera pick up direction by an illumination and this condition will not be changed in the following description) is picked up by this television camera.
As is clear from FIGS. 2A to 2F, since the solid state image pickup elements g and b shown in FIGS. 2C and 2E have no blemish, levels of video signals Vg and Vb from these solid state image pickup elements g and b are equal to levels in which the respective solid state image pickup elements are illuminated on their whole surfaces with a light of uniform brightness. On the other hand, the solid state image pickup element r shown in FIG. 2A has a black blemish at a position shown by a solid arrow in FIG. 2A. Accordingly, in the video signal Vr from this solid state image pickup element r, as shown in FIG. 2B, regardless of the fact that the solid state image pickup element r is illuminated on its entire surface with a light of uniform brightness, the level of the position of the video signal Vr corresponding to a pixel shown by the solid arrow in FIG. 2A becomes substantially zero.
When a video signal from the television camera having incorporated therein the solid state image pickup elements having white and black blemishes shown in FIGS. 1A to 1F and FIGS. 2A to 2F is supplied to and displayed on a monitor receiver, if an iris of the television camera is closed, a white blemish is displayed on the picture screen of the monitor receiver. When the white diffusion plate, for example is picked up by the television camera, a black blemish is displayed on the picture screen of the monitor receiver.
It is substantially impossible to perfectly prevent white and black blemishes of the solid state image pickup element from occurring in the manufacturing-process of the solid state image pickup element. Further, even in the solid state image pickup element where no blemish is discovered in the manufacturing-process, it is frequently observed that a white or black blemish occurs in such solid state image pickup element during such solid state image pickup element is fabricated into a housing of a television camera and is used as the television camera.
Conventionally, as is well known from, for example, Japanese Patent Published Gazette No. 60-34872 the detection of blemish is carried out on each solid state image pickup element, the position of the detected blemish in the solid state image pickup element is detected, and data indicative of the position of blemish is written in a read only memory (ROM). Then, the solid state image pickup element and the ROM are incorporated into the camera apparatus so that, when they are used as the television camera, on the basis of the data indicating the position of blemish read out from the ROM, a video signal output from a pixel having a blemish is interpolated by using output data from other normal pixels.
Incidentally, according to the method in which the solid state image pickup element is inspected independently and address of defective pixel is written in the ROM, the solid state image pickup element and the ROM therefor must be constantly administered perfectly as a pair.
Further, when a new blemish occurs after the solid state image pickup element and the ROM as a pair are incorporated into the housing of the camera apparatus and bought by the user as the television camera, such camera apparatus is returned from the user, the solid state image pickup element and the ROM are again disassembled from the housing of the camera apparatus, and the solid state image pickup element is inspected to detect a defective pixel and an address thereof. If the ROM is a so-called one-time ROM, a new ROM is prepared and if the ROM is an EPROM (electrically programmable ROM), all data are erased and addresses of all defective pixels detected are written in the EPROM. Then, such solid state image pickup element and the ROM as a pair ar assembled into the housing of the camera apparatus and returned to the user.
As described above, in the conventional image defect correcting apparatus, a corresponding relation between the solid state image pickup element and the ROM must be administered, and when new black blemish or new white blemish occurs after the assembly-process, the solid state image pickup element and the ROM must be disassembled from the housing of the camera apparatus and data must be changed. Then, they must be again assembled into the housing of the camera apparatus, which is considerably cumbersome.